The power supply voltage of an electronic system often undergoes a decrease in voltage, especially when being powered by a battery. The voltage of a battery will drop in a curve form when the power of the battery is insufficient, and too low of a voltage possibly leads to an abnormal operation of the system. Thus, an electronic system is usually provided with a circuit for detecting supply voltage to avoid the voltage too low.
FIG. 1 is a schematic diagram of a circuit for detecting supply voltages according to the related art, and as shown in FIG. 1, the circuit for detecting supply voltage consists of a reference voltage circuit 101, a resistor divider circuit 102, a Schmitt trigger comparator 103 and a latch 104, wherein a VDD is divided by resistors R1 and R2 to obtain a voltage VIN, the obtained voltage VIN is connected with the positive input terminal of the Schmitt Trigger comparator 103, and the negative input terminal of the Schmitt Trigger comparator 103 is connected with a reference voltage VREF. The working principle of the circuit lies in that the Schmitt Trigger comparator 103 outputs a high level when the VIN is lower than the VREF, and then the voltage of the output node MRK is at a high level, and on the other side, the Schmitt Trigger comparator 103 outputs a low level when the VIN is higher than the VREF, and then the voltage of the output node MRK is at a low level. Through the voltage division of the resistors R1 and R2, the change of the VDD causes a linear change in the voltage value of the VIN, but the reference voltage is not changed following the change of the VDD, thus realizing a voltage detection function according to the level change of the output node MRK.
It can be seen that, according to the approach of in FIG. 1, a plurality of comparators should be used to detect multiple voltage ranges of a single supply voltage. For instance, if detecting four power supply voltages, four comparators are required.
Due to the power consumption of each comparator, in a circuit for detecting multiple supply voltages, the power consumption of the whole circuit will be undoubtedly huge if multiple comparators are used to detect multiple supply voltages. Power consumption is a very important performance index in a circuit system, and this performance index should be considered by all developers and designers.